.app {
  display: flex;
  width: 800px;
  margin: auto;
  // background: skyblue;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  list-style: none;
}
.left ul {
  display: flex;
  width: 400px;
  padding: 10px;
  flex-wrap: wrap;
}

.left ul li {
  width: 100px;
  height: 100px;
  margin: 10px;
  border: 1px solid #ccc;
  display: flex;
  justify-content: center;
  align-items: center;
  background: #666;
  color: #fff;
  box-shadow: 4px 4px 10px #333;
  &.active {
    background: orangered;
  }
}

.wrapper {
  width: 50px;
  height: 20px;
  background: #ccc;
  border-radius: 2px;
  overflow: hidden;
  .box {
    width: 50%;
    height: 100%;
    background: skyblue;
  }
}

